Integrated method and combined device for pyrolysis, electrode anode production and aluminum production

Abstract

The present invention relates to an integrated process comprising the steps of: (i) pyrolysis of hydrocarbons into carbon and hydrogen, (iia) removing at least part of the carbon produced in step (i) and further processing at least part of the carbon into a carbon-containing electrode, (iib) removing the hydrogen produced in step (i) and using at least part of the hydrogen for providing energy, preferably electricity or heat, for the electrode production in step (iia). In addition, the present invention relates to a combined plant comprising: (a) at least one reactor for a pyrolysis process, (b) at least one reactor for producing electrodes for an aluminum process, (c) a power generation device and / or at least one gas burner, and optionally (d) at least one electrolysis reactor for producing aluminum.

Description

[0001] The present invention relates to an integrated process comprising the steps of: (i) pyrolysis of hydrocarbons into carbon and hydrogen, (iia) removing at least part of the carbon produced in step (i) and further processing at least part of the carbon into a carbon-containing electrode, (iib) removing the hydrogen produced in step (i) and using at least part of the hydrogen for providing energy, preferably electricity or heat, for the electrode production in step (iia). In addition, the present invention relates to a combined plant comprising: (a) at least one reactor for a pyrolysis process, (b) at least one reactor for producing electrodes for an aluminum process, (c) a power generation device and / or at least one gas-fired burner, and optionally (d) at least one electrolysis reactor for producing aluminum.

[0002] Reducing CO2 emissions is an ongoing task for any country in the world. Important sources of CO2 emissions are not only power generation, but also the manufacturing of our daily consumer goods; especially the use of energy-intensive materials such as aluminum. Whether it is beverage cans, packaging, New Year's Eve rockets, toothpaste, car parts, machine parts, aircraft, or even food, aluminum is everywhere.

[0003] The production of aluminum is carried out in an electrolytic cell or tank (known as the Hal-Heroult process). The electrolysis of Al2O3 is carried out in a molten bath of cryolite (Na3AlF6) layered between a carbon anode and molten metal. The aluminum ions in the Al2O3 are reduced to form molten aluminum. The molten aluminum is collected at the bottom of the tank.

[0004] Smelters have high electricity requirements, with energy costs accounting for nearly 40% of the total aluminum costs. Alumina is chemically very stable and requires a lot of electrical energy to reduce, and to keep cryolite molten, heated by resistive electric heating of the cells (the combination of which has a very high power consumption of about 13-14 kWh / kg Al). Energy is also required to preheat the electrodes before they are put into use, which is done using electrical resistances or preheating with gas burners.

[0005] Additionally, unstable power can disrupt production and requiring constant power to keep the process molten, power outages can cause significant downtime. Conversely, the switching of potlines can also cause a sudden drop in demand from power companies, which power suppliers must be able to cope with.

[0006] For this reason, aluminum plants benefit from large scale and are often located near cheap and available sources of electricity or even employ their own generation (captive generation of nuclear, hydrothermal or coal). For example, the new Emirate aluminum plant at Al Taweelah has a connected 3000 MW natural gas fired generation plant to provide electricity for smelting operations alone, while the Santiago Hydro project aims to establish an aluminum smelter that is directly operated by its own hydroelectric power source.

[0007] The carbon electrodes required for aluminium production are either Soderberg anodes, a continuous self-baking type, or more commonly prebaked anodes, which are manufactured in-house and replaced regularly in the smelting cell as they are consumed.

[0008] To produce prebaked anodes, calcined coke, a byproduct from petrochemical refining (petroleum coke), is pulverized and mixed with material from spent electrodes (butts), mixed with pitch and formed into green anodes, which are then baked in large gas furnaces at 1000-1250° C. Material recovered from butts can account for 15-25% of the total electrolytic cell and represents a significant cost and waste reduction.

[0009] In the production of aluminum from Al2O3, carbon anodes are used as reducing agents during an electrolytic process according to the following scheme, where 334 kg of carbon are required per ton of raw aluminum stoichiometrically, but in practice about 400 kgC / ton of Al is required due to carbon deposition.

[0010] 2Al2O3+3C→4Al+3CO2

[0011] Various reactions in the electrolytic cell lead to the consumption of anode carbon. Those that do not lead to metal reduction can lead to excessive carbon consumption, such as charring (O2+C→CO2, where O2 comes from ambient air), carboxyl attack (CO2+C→CO, where CO2 is a product of the aluminum-producing redox reaction) and selective oxidation (dusting). Dusting is a secondary effect of CO2 attack due to the reactivity imbalance between the different coke phases, causing fragments of solid C to fall off.

[0012] In this process, carbon impurities (consisting mainly of metallic trace elements and up to 3% by weight of sulfur) can lead to faster burnout of the electrodes, contamination of the aluminum or SO2 emissions.

[0013] The cost of carbon anodes accounts for 15-20% of the total cost of aluminum electrolysis production. Therefore, the quality of carbon anodes is very important and significantly affects the energy consumption and environmental impact of aluminum electrolysis.

[0014] The required petroleum coke is purchased directly from the refinery (usually after calcination). Due to the size and high throughput of the anodes and the need to recycle a significant portion of the butts, smelters maintain anode production and in-house baking with specialized equipment and cranes to move large anodes between the forming, baking and smelting steps. Keeping the baking in-house also allows the smelter to maintain control over the baking conditions, which can affect the performance of the electrolytic cell.

[0015] Anode production for aluminum processes is described, for example, in “Anode Manufacture, Raw Materials Formulation and Processing Parameters”, Kristine L. Hulse, R&D Carbon.

[0016] The continued growth in demand for aluminum metal coupled with declining and fluctuating aluminum grade coke quality as the density and purity of the affected coke varies makes it more challenging for anode manufacturing units to achieve consistent anode quality. Lower quality grades of coke are more reactive, resulting in higher carbon consumption at the smelter.

[0017] About 95% of the SO2 emissions generated by smelters can be attributed to the sulfur found in the incoming petroleum coke used in anode production. As a result, environmental regulations are aimed at reducing sulfur emissions, and coke suppliers are offering higher sulfur materials. Low sulfur coke materials are becoming less available on the market and prices are steadily rising. In addition, the sulfur content of many traditional "high sulfur" anode grade green cokes is increasing. Five years ago, high sulfur anode grade green coke was considered to be coke with a sulfur content of 3-4%. Today, more typical levels are 4-6%.

[0018] The price difference between a barrel of sweet crude oil and sour crude, known as the "sweet sour spread," has led more refineries to process cheaper, higher-sour crude. The coke produced from these higher-sour crudes has higher levels of sulphur and metallic impurities (particularly vanadium and nickel). More of this coke is being used by calciners to meet growing demand from the aluminium industry.

[0019] Because aluminum smelters do not significantly change coke sulfur specifications due to smelter environmental constraints, high coke sulfur levels must be offset by blending with lower sulfur coke. As a result, the difference in sulfur content of the cokes used in a typical anode mix is ​​increasing, with cokes with sulfur contents of 1-2% being blended with cokes with sulfur contents as high as 4-6% to achieve smelter anode coke specifications of 1.0-3.5%.

[0020] With the projected growth rates in primary aluminum production, the industry will have no choice but to use these higher sulfur content coke blends. The sulfur content of high sulfur cokes used in blends is increasing and will likely continue to increase.

[0021] In addition to sulfur requirements, the primary aluminum industry is also faced with the task of reducing CO2 emissions.

[0022] The use of pyrolysis of hydrocarbons into carbon and hydrogen has been disclosed as a possibility to obtain hydrogen with less or even no CO2 emissions; see, for example, WO 2013 / 004398. In addition, pyrolysis is also described, for example, in DE1266273B, US 2002 / 0007594, WO2014 / 090914 and PCT / EP2019 / 051466. It is described that the carbon produced can be used in the aluminum industry (see EP18184459.8, filed on July 19, 2018) or for power generation (see EP 2987769), and the hydrogen can be used in the chemical industry or for any power generation. So far, no combined plant has been disclosed in terms of integrated aluminum production.

[0023] If pyrolysis hydrogen is used in the chemical industry, it must be purified to >99%, and even higher purities are required in fuel cell applications. Typically, pyrolysis hydrogen off-gas may contain only 30-90% hydrogen, with the remainder being mainly unconverted methane. Purification can be performed by pressure swing adsorption, which requires significant construction and operating costs for the pyrolyzer.

[0024] In short, the underlying challenges are: (i) ensuring a sufficiently pure carbon source and a stable supply, (ii) reducing CO2 and SO2 emissions during electrode production and aluminum production processes driven by political incentives to reduce CO2 and SO2, and (iii) ensuring a stable and economical supply of electricity, especially considering the increasing share of renewable, variable energy.

[0025] The present invention relates to an integrated process comprising the following steps: (i) pyrolysis of hydrocarbons into carbon and hydrogen, (iia) removing at least part of the carbon produced in step (i) and further processing at least part of the carbon into a carbon-containing electrode and optionally using the produced carbon-containing electrode for producing aluminum in step (iii), (iib) removing the hydrogen produced in step (i) and using at least part of the hydrogen for generating and providing energy, preferably electricity or heat, for the electrode production in step (iia) and / or the aluminum production in step (iii).

[0026] Preferably, the present invention relates to an integrated process comprising the following steps: (i) pyrolysis of hydrocarbons into carbon and hydrogen, (iia) removing at least part of the carbon produced in step (i) and further processing at least part of the carbon to form a carbon-containing electrode, (iii) using the electrode produced in step (iia) for the production of aluminum, in particular in Hall-Heroult electrolysis, (iib) removing the hydrogen produced in step (i) and using at least part of the hydrogen for generating and providing energy, preferably electricity or heat, for the electrode production in step (iia), the aluminum production in step (iii) and / or the pyrolysis process in step (i).

[0027] The main feature of the present invention is that the generated carbon and byproduct hydrogen can be beneficially used for electrode and / or aluminum production. Therefore, the present invention is a material and energy integration of pyrolysis and electrode and / or aluminum production, while solving the requirements of reducing SO2 and CO2.

[0028] The pyrolysis of step (i) can be carried out as described in the literature and in a manner known to those skilled in the art (see, for example, Muradov, Nazim. "Low to near-zero CO2 production of hydrogen from fossil fuels: Status and perspectives.", International Journal of Hydrogen Energy 42.20 (2017): 14058-14088). Typically, gaseous hydrocarbon compounds are decomposed at a temperature of 1000-2500 K and a pressure of 0.5-5000 kPa (abs). A substrate is typically used; the substrate can be porous or non-porous and can be a supported substrate (pre-installed part) or a granular and powdered material in the reactor. The latter can be realized in the form of a fixed bed, a moving bed, a fluidized bed or an entrained flow. Pyrolysis is not limited to a specific energy supply; fossil combustion, electric heating and / or plasma-driven production reactors are all possible.

[0029] The substrate is advantageously thermally stable in the range of 500-2000°C, preferably 1000-1800°C, further preferably 1300-1800°C, more preferably 1500-1800°C, in particular 1600-1800°C.

[0030] The substrate is advantageously between 10 S / cm and 10 5 The range between 1000 S / cm is conductive.

[0031] Useful thermally stable substrates advantageously include carbonaceous materials such as coke, silicon carbide and boron carbide. Optionally, the substrate has been coated with a catalytic material. These thermal substrate materials may have different expansion properties than the carbon deposited thereon.

[0032] The granulate particles have regular and / or irregular geometric shapes. Regularly shaped particles are advantageously spherical or cylindrical.

[0033] The granules advantageously have a particle size, ie an equivalent diameter, determinable by sieving using a specific sieve size, of 0.05 to 100 mm, preferably 0.1 to 50 mm, more preferably 0.2 to 10 mm, in particular 0.5 to 5 mm.

[0034] It is also advantageous to use carbonaceous materials, for example in pellet form. Carbonaceous pellet materials in the present invention are understood to mean materials which advantageously consist of solid particles having at least 50% by weight, preferably at least 80% by weight, further preferably at least 90% by weight, in particular at least 90% by weight of carbon.

[0035] In the method of the present invention, a variety of different carbonaceous granular materials can be used. Such granular materials can, for example, be mainly composed of charcoal, coke, coke powder and / or mixtures thereof. In addition, the carbonaceous granular material can contain 0-15% by weight, preferably 0-5% by weight, of metals, metal oxides and / or ceramics based on the total mass of the granular material.

[0036] The expression "pyrolytic carbon" encompasses solid carbon produced by pyrolysis of light carbon under oxygen-free conditions. Preferred pyrolytic carbon for electrodes, preferably anodes, is high density solid elemental carbon produced by deposition on carbon pellets. This is superior to thermal black produced by thermal / plasma processes or nanostructured carbon grown on metal / oxide catalysts.

[0037] A wide range of microstructures, such as isotropic, layered, matrix nucleated and different residual hydrogen contents can appear in pyrolytic carbon, depending on the deposition conditions (temperature, type, concentration and flow rate of source gases, surface area of ​​the underlying substrate, etc.).

[0038] Typically the density of pyrolytic carbon is 1.6-2.3 g / cc, preferably 1.8-2.2 g / cc (actual density in xylene, ISO 8004).

[0039] The impurities of pyrolytic carbon are usually: 0-1%, preferably 0-0.5%, more preferably 0-0.1% S. 0-1000ppm, preferably 0-500ppm Fe, 0-250ppm, preferably 0-100ppm Ni, 0-450ppm, preferably 0-250ppm, more preferably 0-100ppm V. 0-200ppm, preferably 0-100ppm Na.

[0040] Typically, the particle size of the pyrolytic carbon after pyrolysis is at least 5% by weight>1 mm, preferably 50% by weight>0.5 mm.

[0041] Typically the crystal size (XRD) of the pyrolytic carbon is 20-60 angstroms, preferably 30-50 angstroms (XRD, ISO 20203).

[0042] Typically the porosity of the pyrolytic carbon pellets is less than 15%, preferably less than 10%, most preferably less than 5% (Hg porosimetry, DIN 66133).

[0043] The specific surface area of ​​pyrolytic carbon is usually measured by Hg porosimetry (DIN 66133) and is 0.001-5 m 2 / g, preferably 0.01-2m 2 / g.

[0044] In step (iia), at least part of the pyrolytic carbon produced in step (i) is removed from the pyrolysis reactor. The removed carbon is at least partially further processed into a carbon-containing electrode, preferably an anode. Methods for producing electrodes, preferably anodes, for aluminum production are well known in the art (see, for example, "Anode Manufacture, Raw Materials Formulation and Processing Parameters, Kristine L. Hulse, R&D Carbon"). The use of pyrolytic carbon as a mixed material in the anode is described in European patent application EP 18184459.8 filed on July 19, 2018.

[0045] Typically 35-95 wt %, preferably 50-80 wt % of the total weight of the anode formulation is a mixed composition of carbon materials, in particular petroleum coke. Typically 0-40 wt %, preferably 15-30 wt % of the total weight of the anode formulation is anode scrap and / or waste. Typically 5-25 wt %, preferably 10-20 wt %, even more preferably 13-18 wt % of the total weight of the anode formulation is a binder.

[0046] Preferably, the carbon electrode comprises a mixed composition comprising a mixture, wherein (i) the content of petroleum coke is 30-98 weight percent, more preferably 50-95 weight percent, more preferably 70-95 weight percent, more preferably 85-95 weight percent, and even more preferably 90-95 weight percent, based on the total weight of the mixed composition, and (ii) the content of pyrolytic carbon is 2-70 weight percent, more preferably 5-50 weight percent, more preferably 5-30 weight percent, more preferably 5-15 weight percent, and even more preferably 5-10 weight percent, based on the total weight of the mixed composition.

[0047] Preferably, calcined petroleum coke (CPC) is used as petroleum coke (Predel, H. (2000). Petroleum coke. Ullmann's Encyclopedia of Industrial Chemistry). Preferably, the sulfur content of petroleum coke is 0-10 wt %, more preferably 0.5-8.5 wt %, more preferably 1.5-7.0 wt %, based on the total weight of petroleum coke. Petroleum coke is usually abbreviated as petroleum coke.

[0048] Preferably, the mixed composition contains at least two particle size fractions: (i) granules above 0.5 mm and (ii) fines below 0.5 mm. Typically the granule size fraction is 0.5-16 mm, preferably 0.5-8 mm. Typically, the fines size fraction is 0.005-0.5 mm.

[0049] Based on total pyrolytic carbon: preferably 30-100 wt %, even more preferably 50-100 wt %, more preferably 70-100 wt %, more preferably 90-100 wt %, even more preferably 95-100 wt %, even more preferably all of the pyrolytic carbon of the mixed composition is within the pellet size fraction.

[0050] Preferably 30-80 wt%, more preferably 40-70 wt%, even more preferably 50-65 wt% of the particles have a granular particle size, and 20-70 wt%, more preferably 30-60 wt%, even more preferably 35-50 wt% of the particles have a fine particle size.

[0051] Pyrolytic carbon can be added to petroleum coke before crushing, screening and classification, or directly added to the crushed, screened and classified petroleum coke aggregate. Preferably, pyrolytic carbon can be added directly to the existing anode feedstock stream.

[0052] The mixed composition of pyrolytic carbon and petroleum coke and anode scraps and / or waste is preferably preheated, preferably to a temperature of 100-175°C (to melt the binder), and mixed with a binder (typically coal tar pitch), which is preferably also preheated to melt. The preheated anode formulation is preferably pressed into final shape to ensure that the pressed anode block retains its structural form. The green compact is preferably then heated at an elevated temperature, for example 1000-1250°C, to form a baked anode, which is then suitable for consumption in an electrolytic cell.

[0053] Preferably, the carbon anode produced according to the present invention provides one or more of the following performance characteristics, preferably all mentioned parameters:

[0054] The green density is preferably at least 1.50 g / cm3 (ISO 12985-1). The specified range for CPC anodes is 1.54-1.66 g / cm 3 (ISO 12985-1).

[0055] The calcined density is preferably at least as high as 1.50 g / cm 3 (ISO 12985-1). The specified range for CPC anodes is 1.50-1.58 g / cm 3 (ISO 12985-1).

[0056] Thermal shock and mechanical resistance are preferably above 6 MPa (ISO 12986-1), while 6-11 MPa are typical values ​​for CPC-based anodes.

[0057] The compressive strength is preferably higher than 25 MPa (ISO 18515).

[0058] The electrical resistance is preferably below 80 μΩm. 55-80 μΩm is a typical industrial range. In the case of air reactivity, the so-called air residual after a test reaction with air is preferably below 85% by weight, more preferably 70% by weight (70-85 is typical, ISO 12989-1). For CO2 reactivity, the so-called CO2 residual after a test reaction with CO2 is preferably below 95% by weight, more preferably 80% by weight (80-95 is conventional, ISO 12988-1).

[0059] Preferably, 80-100 wt% of the carbon produced in step (i) is further processed into a carbon-containing electrode; more preferably, 90-100 wt% of the carbon produced in step (i) is further processed into a carbon-containing electrode; even more preferably, all of the carbon produced in step (i) is further processed into a carbon-containing electrode. The capacity of the pyrolysis reaction can be easily adapted to the carbon requirements of electrode production.

[0060] Additionally, another portion of the removed pyrolysis carbon produced in step (i) can be burned to heat other parts of the integrated process, since the gas burner can be operated with carbon powder.

[0061] Additionally, another portion of the removed pyrolytic carbon may be sold for use in other applications, such as for use in steel or for electrode production at another industrial site.

[0062] In step (iii), the electrode produced in step (iia), preferably the anode, is used for aluminum production, in particular for Hall-Heroult electrolysis. Hall-Heroult electrolysis is well known in the art (see, for example [Grjotheim K, Kvande H, ed., Introduction to Aluminium Electrolysis—Understanding the Hall-Heroult Process. 2nd edition, Dödsseldorf, Germany: Aluminium-Verlag; 1993: 199-217]).

[0063] In step (iib), the hydrogen produced in step (i) is removed from the pyrolysis reactor. At least part of the hydrogen is used to generate energy, preferably electricity or heat, both of which are well known in the prior art. The energy generated is provided for the electrode production in step (iia), the aluminum production in step (iii) and / or the pyrolysis process in step (i).

[0064] Control over whether hydrogen is used to generate heat or electricity may be subject to the availability of external regenerative excess power capacity (see, for example, WO 2014 / 090914). Furthermore, control over whether hydrogen is used to generate heat or electricity depends on the energy mix of the smelter, aluminum production.

[0065] The hydrogen produced in step (i) can be used preferably as a fuel or in a mixture with conventional fuels (mainly natural gas) for any heating step in the aluminum production process, electrode production and / or pyrolysis process. Preferably, at least a portion of the hydrogen produced in step (i) is used to enrich the natural gas in the combustion furnace for heating the electrode production in step (iia).

[0066] Preferably 5-50% by volume, even more preferably 10-40%, even more preferably 20-30% of the natural gas used as fuel may be replaced by the hydrogen produced in step (i).

[0067] Preferably, up to 30% of the natural gas can be replaced by the hydrogen produced in step (i). Usually existing burners do not need to be changed. If hydrogen is mixed into existing natural gas burners, combustion can be improved and emissions can be reduced. Replacing 30% of the natural gas in a generator or gas burner with hydrogen can reduce CO2 emissions by up to 18%. Germany and the Netherlands have used hydrogen-enriched natural gas. Maughan et al. disclosed that natural gas containing 10-20% by volume H2 will also have lower NOx emissions (Maughan, JR, JH Bowen, DH Cooke and JJ Tuzson, "Reducing Gas Turbine Emissions through Hydrogen-Enhanced, Steam-Injected Combustion", Proceedings of ASME Cogen-Turbo Conference, pp. 381-390, 1994).

[0068] A hydrogen-rich fuel is preferably used for the burner in the firing step of the electrode in step (iia) and / or the electrode preheating in step (iii). It is known in the art to convert existing burners based on natural gas to fuels based on hydrogen and / or natural gas.

[0069] Alternatively, a portion of the hydrogen produced in step (i) is used to heat the pyrolysis; either as a fuel for a burner or to generate electricity.

[0070] Alternatively, a portion of the hydrogen produced in step (i) is used to generate electricity for heating the smelting unit (iii) for aluminium production.

[0071] Furthermore, a portion of the hydrogen produced in step (i) is used to generate electricity to heat the electrode firing step in step (iia). Well-known facilities for preheating and firing electrodes can be easily adapted to use electrical heating.

[0072] The hydrogen produced in step (i), i.e. the pyrolysis hydrogen off-gas, contains about 30 to 90% by volume hydrogen, with the remainder being mainly unconverted methane. If this pyrolysis hydrogen off-gas is used to mix with natural gas in a burner system, e.g. for power generation or a gas burner, then there is no need to remove excess methane from the hydrogen, and the CO2 reduction benefits of hydrogen-rich natural gas can still be provided.

[0073] Preferably, the hydrogen produced in step (i) is used for mixing with natural gas in a burner system without any purification.

[0074] Furthermore, part of the hydrogen produced in step (i) may be exported, for example to a nearby industrial plant or site, such as an iron production site, in particular for direct reduction of iron ore, or for use in other chemical processes requiring hydrogen as a reducing agent.

[0075] Furthermore, part of the hydrogen produced in step (i) may be fed into the natural gas grid.

[0076] The three plants can be easily connected by a person skilled in the art. Preferably, the pyrolytic carbon can be added directly to an existing electrode, preferably anode feed stream. Preferably, the hydrogen produced in step (i) can be easily mixed with a natural gas pipeline.

[0077] Furthermore, the present invention relates to a combined plant comprising: (a) a reactor for a pyrolysis process, (b) a reactor for an electrode, preferably an anode, for the production of an aluminium process, (c) a power generation device and / or at least one gas burner, and optionally (d) an electrolysis reactor for the production of aluminium.

[0078] Preferably, a power generation device is integrated in the combined device. The power generation device for generating electricity is preferably a gas turbine, a boiler or a hydrogen fuel cell. The turbine and / or boiler can preferably be used without any treatment and / or separation of the feed gas.

[0079] If the plants are located within a radius of about 50-100km, there are still benefits of joint planning.

[0080] advantage:

[0081] One advantage of this method is that methane (natural gas) is a carbon source that is easier to transport than petroleum coke. Natural gas can be transported by pipeline and is readily available in locations where petroleum coke may not exist. Petroleum coke is primarily supplied by refineries and shipped by ship to smelters located near cheap electricity such as hydroelectric power and may not be near a seaport.

[0082] An additional advantage is that pyrolysis coke is very clean and the integrated pyrolysis process results in a stable supply of carbon. The carbon is not subject to the fluctuations in cost, purity and properties seen in the petroleum coke market. This stability has significant operational benefits for smelters.

[0083] Additionally, smelters produce large amounts of CO2 in their processes and will benefit from reducing emissions, with H2 being used for roasting instead of traditional gas burners. Hydrogen can also be used for CO2-free power generation.

[0084] For example, Australia will give smelters cheaper electricity if they use a higher percentage of renewable energy (“Energy efficiency best practice in the Australian aluminium industry”, Department of Industry, Science and Resources—Australian Government, July 2000).

[0085] Since the smelter already blends a portion of the butts, the smelter is already able to handle a mixed stream, internal and external carbon supply.

[0086] Furthermore, when H2 is produced by pyrolysis, the hydrogen must be purified to >99% for use in chemical processes, and even higher purities are required for fuel cell applications. Typically the exhaust gas may be only 30-90% hydrogen, the remainder being mainly unconverted methane. Purification is typically performed by pressure swing adsorption, which requires significant construction and operating costs for the pyrolyzer. In contrast, using the exhaust gas from pyrolysis to blend into natural gas in a burner system such as for power generation or gas burners does not require removal of excess methane from the hydrogen and still provides the CO2 reduction benefits of hydrogen-enriched natural gas.

[0087] In summary, the present invention provides the following economic and technical advantages: (i) integrated production and use of pyrolytic carbon to produce electrodes, with potentially advantageous properties in aluminum production, such as lower electricity and carbon consumption and reduced CO2 and SO2 emissions; (ii) reduced demand for petroleum coke and increased tolerance to low-grade petroleum coke; (iii) integrated supply and utilization of electrical energy and thereby reduced electricity costs; (iv) integrated utilization of hydrogen through combustion and thereby reduced methane / natural gas combustion and CO2 emissions; (v) no need for third parties, such as customers of by-products such as syngas.

[0088] In view of (v), the integration within the complex is complete and does not require the coupling or decoupling of additional material and energy flows. This means that the integration of pyrolysis in electrode production does not depend on the demand for any by-product streams by third parties.

[0089] Figure 1 A simplified diagram of the combined apparatus is shown:

[0090] [1] is the anode baking step, [2] is the Hall-Herout smelting process, [3] is the combined methane pyrolysis and power generation unit, [4] is the methane pyrolysis reactor, [5] is the exhaust gas from the power turbine, [6] is the combined recycled natural gas / H2 turbine, [7-11] are the anode manufacturing / baking steps, where [7] is heating, [8] is mixing, [9] is shaping,

[10] is green anodes, and

[11] is the anode baking step.

[12] is the natural gas from the grid for the anode baking step and

[13] is the natural gas to the pyrolysis reactor. The pyrolysis carbon from the reactor

[14] is combined with

[15] fresh petroleum coke from the refinery and

[16] recycled electrode butts.

[17] is pitch.

[18] is CO2 and emissions from the anode baking step, and

[19] is the combined emissions including CO2 / SO2 from electrolysis.

[20] H2-rich product gas from the pyrolysis reactor,

[21] natural gas added to anode baking

[12] , the remainder

[22] used for power generation.

[23] is the electricity used in pyrolysis, and

[24] is the electricity to the smelter.

[25] is the combined grid and self-generated electricity and

[26] is the electricity used for anode manufacturing and baking. Example

[0091] Embodiment 1:

[0092] An aluminum smelter with a historical average of 1.36 kWh / kg aluminum product in the anode roasting step is supplied by direct combustion of natural gas, replacing 50% of its anode carbon with pyrolytic carbon. This directly reduces the sulfur emissions of the smelting step by 50%. Methane pyrolysis produces an additional 0.07 kg H2 and 0.88 kWh of energy is required for pyrolysis per kg of final aluminum production. Direct combustion of the hydrogen by-product is used to heat the pyrolysis step. Because the by-product gas containing hydrogen is mainly methane, no purification is required if the hydrogen is used to burn the burner. After heating the pyrolysis reactor, the remaining H2 is used to heat the anode roasting step, completely replacing the natural gas demand in roasting and resulting in a net reduction of 500 kg CDE (carbon dioxide emissions) per ton of aluminum. An excess of 0.12 Nm3 of H2 remains per kg Al and can be sold or burned or used elsewhere in the system.

[0093] Embodiment 2:

[0094] As in Example 1, an aluminum smelter with a historical average of 1.36 kWh / kg Al product on the anode roasting step is supplied by direct combustion of natural gas, replacing 50% of its anode carbon with pyrolytic carbon. This directly reduces the sulfur emissions of the smelting step by 50%. Methane pyrolysis produces an additional 0.07 kg H2 and 0.88 kWh of energy is required for pyrolysis per kg of final aluminum production. Direct combustion of the hydrogen byproduct is used to heat the pyrolysis step and the remaining H2 is mixed with natural gas and directly used in the existing combined cycle power generation turbine. The resulting electricity is used to provide electricity for the smelter. The total pyrolytic hydrogen produced replaces 15% of the total natural gas by volume. 30% rich hydrogen can be used with little or no changes to existing burners. This results in a direct reduction of 350 kg / ton Al CDE (CO2 emissions).

[0095] Example 3

[0096] As in Example 2, an aluminum smelter with a historical average of 1.36 kWh / kg Al product on the anode roasting step, supplied by direct combustion of natural gas, replaces 50% of its anode carbon with pyrolytic carbon. This directly reduces the sulfur emissions of the smelting step by 50%. Methane pyrolysis produces an additional 0.07 kg H2 and 0.88 kWh of energy is required for pyrolysis per kg of final aluminum production. The hydrogen by-product is mixed with natural gas and directly used in the existing combined cycle power generation turbine. The resulting electricity is used to provide electricity for the pyrolysis reactor and the smelter. The total pyrolytic hydrogen produced replaces 20% of the total natural gas by volume. This results in a direct reduction of 170 kg / ton Al CDE (CO2 emissions).

Claims

1. An integrated process comprising the steps of: (i) pyrolyzing hydrocarbons into carbon and hydrogen, (iia) removing at least part of the carbon produced in step (i) and further processing at least part of the carbon into a carbon-containing electrode and optionally using the produced carbon-containing electrode for producing aluminum in step (iii), (iib) removing the hydrogen produced in step (i) and using at least part of the hydrogen as a mixture with natural gas in a burner system for any heating step in the electrode production in step (iia) and / or the aluminum production in step (iii), wherein the carbon electrode comprises a mixed composition, the mixed composition comprising a mixture, wherein (i) the content of petroleum coke is 30-98 weight%, based on the total weight of the mixed composition, and (ii) the content of pyrolytic carbon is 2-70 weight%, based on the total weight of the mixed composition.

2. A method according to claim 1, wherein at least part of the hydrogen produced in step (i) is used to charge natural gas in a burner to provide energy.

3. The process according to claim 1, wherein 5-30% of the natural gas used as fuel is replaced by the hydrogen produced in step (i).

4. The process according to claim 2, wherein 5-30% of the natural gas used as fuel is replaced by the hydrogen produced in step (i).

5. The method according to claim 1, wherein at least part of the hydrogen produced in step (i) is used to generate electricity to heat the pyrolysis of step (i) and / or the smelting unit of the aluminum production of step (iii).

6. The method according to claim 1, wherein 80-100 wt. % of the carbon produced in step (i) is further processed into a carbon-containing electrode.

7. The method according to claim 2, wherein 80-100 wt. % of the carbon produced in step (i) is further processed into a carbon-containing electrode.

8. The method according to claim 3, wherein 80-100 wt% of the carbon produced in step (i) is further processed into a carbon-containing electrode.

9. The method according to claim 4, wherein 80-100 wt. % of the carbon produced in step (i) is further processed into a carbon-containing electrode.

10. The method according to claim 5, wherein 80-100 wt% of the carbon produced in step (i) is further processed into a carbon-containing electrode.

11. The method according to any one of claims 1 to 10, wherein the substrate is used in the pyrolysis process of step (i) in the form of a fixed bed, a moving bed, a fluidized bed or an entrained flow.

12. A process according to any one of claims 1 to 10, wherein the carbon produced in step (i) has a density of 1.6 to 2.3 g / cc.

13. The process according to claim 11, wherein the carbon produced in step (i) has a density of 1.6-2.3 g / cc.

14. A process according to any one of claims 1 to 10, wherein the particle size of the carbon produced in step (i) has at least 50% by weight greater than 0.5 mm.

15. A process according to claim 13, wherein the particle size of the carbon produced in step (i) has at least 50% by weight greater than 0.5 mm.

16. The method according to any one of claims 1 to 10, wherein a portion of the hydrogen produced in step (i) is exported to a neighboring industrial plant for use in a chemical process requiring hydrogen as a reducing agent.

17. The method according to claim 15, wherein a portion of the hydrogen produced in step (i) is exported to a nearby industrial plant for use in a chemical process requiring hydrogen as a reducing agent.

18. The method according to any one of claims 1 to 10, wherein the electrode produced in step (iia) is used for producing aluminium in step iii.

19. A method according to claim 17, wherein the electrode produced in step (iia) is used to produce aluminum in step iii.

20. The method according to any one of claims 1 to 5, wherein the carbon produced in step (i) is further processed in a carbon-containing anode.

21. The method according to claim 1, wherein the carbon and petroleum coke produced in step (i) and the butts and / or waste are preheated, mixed with a binder, pressed and heated to form a baked anode.

22. The method according to claim 1, wherein the hydrogen is at least partly used without any purification as a mixture with natural gas in a burner system for any heating step in the electrode production in step (iia) and / or the aluminum production in step (iii).

23. A combined apparatus for a method according to any one of claims 1 to 22, comprising: (a) a reactor for a pyrolysis process, (b) a reactor for electrodes for an aluminum production process, (c) at least one gas burner, and optionally (d) an electrolysis reactor for the production of aluminum.

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